Coreless and spirally wound non-woven filter element

ABSTRACT

A homogeneous mixture of a base and a binder material or fiber that is compressed to form a mat or sheet of selected porosity. The binder material has at least a surface with a melting temperature lower than that of the base fiber. The sheet is formed into a selected geometric shape and thermally fused to bind the base fiber into a porous filter element. The preferred shape is a helically wound tube of plural sheets, each sheet being self-overlapped and compressed to overlap another sheet. Each sheet preferably heated and compressed individually and the sheets may be selected to have different porosities and densities. The binder fiber is selected from the group consisting of thermoplastic and resin, and the base fiber is selected from the group consisting of thermoplastic and natural.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to filter elements and to the machines andmethods used in their manufacture.

2. Background Information

There are machines used to manufacture tubular filter elements in acontinuous process. U.S. Pat. No. 4,101,423 discloses a tubular filterelement made on a single-stage multiple winding machine of helicallywound and overlapping layers such as an inner layer of high wetstrength, highly porous paper, a second layer of thin microporousfiltration material of a sterilizing grade and an outer layer of aporous sheet of expanded polyethylene and an outer porous layer tosupport the filtration material. The layers are wrapped on a fixedmandrel to be self-overlapping in a single layer overlap and advance inunison along the mandrel as they are wrapped so that there is norelative motion between the adjacent layers of the laminate. An adhesivematerial that blocks the passage of the particulate matter and bacteriabeing filtered seals the second filtration layer in the region ofoverlap. The ends of the tubular laminate construction are impregnatedover a predetermined length adjacent to each edge of the constructionwith a suitable sealing adhesive material such as a polyurethane pottingcompound. When the adhesive material cures, the end portions providemechanical support for the tube while blocking the passage of the fluidor the particulate and bacterial contaminants. (See Col. 5, Ins. 4-26.)

A circularly wound spiralled chromatographic column is shown in U.S.Pat. No. 4,986,909. Here, a sandwich or laminate of alternating layersof swellable fibrous matrix in sheet form and layers of spacer means,with the periphery of the sandwich is compressed into a fluid-tightconfiguration. Typically, the peripheral edges of alternating discs ofswellable fibrous matrix and spacer means are joined. Preferably, thefibrous matrix contains or has bonded therein a thermoplastic polymericmaterial, as does the spacer means. The edges may be joined byappropriate heating, e.g. sonic welding. (See Col. 10, Ins. 40-61.)

Another spirally, circularly wound filter element is disclosed in U.S.Pat. No. 5,114,582 and comprises one or more filter elements spirallywound on a cylindrical permeate transport tube. Each filter elementcomprises a heat-sealed membrane element and a feed spacer. (SeeAbstract.)

A process for the manufacture of porous tubes of high permeability madefrom a carbon--carbon composite material in a strip of mat spirallywound on a mandrel is disclosed in U.S. Pat. No. 5,264,162. Porous tubesare made from said material by winding over a mandrel a nonwoven sheet,made from a carbon fiber precursor, followed by compression and hotstabilization of the assembly. The sheet is impregnated by a resin,followed by a thermal carbonization treatment of the resin. Tubes areobtained having a high permeability, small pore diameter and an innersurface of low rugosity. (See Abstract.) Also disclosed is the use ofsuccessive mat layers, making it possible to obtain, in the final tube,pore diameters which increase in the direction of the flux to befiltered, generally from the inside towards the outside of the tube. Itis advantageous that these pore diameters are substantially in a ratioof 10 between one layer and the next, which may be obtained by adjustingthe density of the mat and/or the diameter of the fibers. (See Col. 4,Ins. 10-20.)

A helically wound, single wrap filter element is disclosed in U.S. Pat.No. 5,409,515, including a porous membrane of a polytetrafluoroethyleneand one or more sheets composed of fibers made of a thermally meltingsynthetic resin. (See Abstract.) The sheets are thermally fused over aselected length. (See Col. Ins. 40-46.)

SUMMARY OF THE INVENTION

It is the general object of the invention to provide an improved filterelement made with improved methods and machines for their manufacture.

This object is achieved with a filter element made of at least onenonwoven fabric of a homogeneous mixture of a base and a binder materialthat is compressed to form a mat or sheet of selected porosity. Thebinder fiber has at least a surface with a melting temperature lowerthan that of the base fiber. The sheet is formed into a selectedgeometric shape and heated to thermally fused to bind the base fiberinto a porous filter element. The preferred shape is a helically woundtube of plural sheets, each sheet being self-overlapped and compressedto overlap another sheet. Each sheet preferably heated and compressedindividually and the sheets may be selected to have different porositiesand densities. The binder material is selected from the group consistingof thermoplastic and resin, and the base material is selected from thegroup consisting of thermoplastic and natural.

The machinery preferably used to produce the filter element employs thea method of manufacture that includes the step of forming a nonwovenfabric of a homogeneous web of a base fiber and a binder fiber, asexplained above, compressed to form a sheet of selected porosity. Pluralsheets of nonwoven fabric are wrapped helically on a multi-stationwrapping machine with individual belts, each powered by a capstan toform individual layers that overlap to form a laminate. The tension ofeach belt is selected to compress each layer a selected degree. Eachlayer is heated to accomplish the thermal fusion step. Cooling fluid ispumped through the hollow mandrel to prevent excessive heat build-up inthe mandrel. The machine is controlled by a computer, which receivesinput signals that adjust machine functions such as the capstan drivingmotor speed, the tensions of the sheet wrapping belts, the temperatureof the heater array used to accomplish thermal fusion of each layer, andthe flow of cooling fluid flowing through the hollow mandrel.

The above as well as additional objects, features, and advantages of theinvention will become apparent in the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view in partial section of the preferredembodiment of the invention that illustrates a multi-overlapped corelessfilter element made in a four station wrapping machine using four rollsof selected nonwoven fabric.

FIG. 2 is a cross-sectional view that illustrates the multi-overlappedcoreless filter element of FIG. 1 being formed on a hollow mandrel.

FIG. 3 is a schematic top view of three stations of the machine used tomanufacture the filter element of FIG. 1.

FIG. 4 is a perspective view that illustrates the preferred embodimentof a multi-stage winding machine used to that produce the filter elementof FIG. 1.

FIG. 5 is a block diagram of the preferred nonwoven fabric manufacturingprocess used to produce the filter element of FIG. 1.

FIG. 6 is a schematic diagram of a computer based system used to controlthe winding machine of FIG. 4.

FIG. 7 is a schematic diagram of a control system used to control thetension of the fabric feed belt of the multi-stage winding machine ofFIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 of the drawings, the numeral 11 designates amulti-overlapped coreless filter element constructed according to theprinciples of the invention. It includes a first multi-overlappednonwoven fabric strip 13, a second multi-overlapped nonwoven fabricstrip 15, a third multi-overlapped nonwoven fabric strip 17, and afourth multi-overlapped nonwoven fabric strip 19. Each fabric strip 13,15, 17, 19 is spirally or helically wound in overlapping layers to formoverlapping bands 14, 16, 18, 20, respectively. The radially interiorsurface 21 of band 14 forms the periphery of an axially extendingannular space that extends from one end 25 of the filter element to theoppositely facing end 27 of the filter element 11. In the drawings thethickness of the fabric is exaggerated.

In FIG. 2 of the drawings, the numeral 47 designates a hollowcylindrical mandrel with an annular exterior surface 49 and an annularinterior surface 51, said annular interior surface 51 forming theperiphery of a cylindrical channel 53, through which flows a liquid orgas heat exchange medium (not shown). Band 14 of multi-overlappednonwoven fabric strip 13, is shown overlapped by band 16 ofmulti-overlapped non-woven fabric strip 15, which in turn is overlappedby band 18 of multi-overlapped nonwoven fabric strip 17, which is thenoverlapped by band 20 of multi-overlapped nonwoven fabric strip 19.

As shown in FIG. 3 of the drawings, only three stages are shown of themulti-stage winding machine shown in greater detail in FIG. 4. In FIG.3, a first compression belt 55 is shown wrapping, in a multi-overlappedfashion, nonwoven fabric strip 13 about the hollow mandrel 47. A secondcompression belt 57 is shown wrapping, in a multi-overlapped fashion,nonwoven fabric strip 15 about multi-overlapped nonwoven fabric strip13. A third compression belt 59 is shown wrapping, in a multi-overlappedfashion, non-woven fabric strip 17 about multi-overlapped nonwovenfabric strip 15. A first heater array of preferably infrared heaters 63is shown in a position to apply heat, simultaneously with thecompression of compression belt 55, to multi-overlapped nonwoven fabricstrip 13. A second heater array of infrared heaters 65 is shown in aposition to apply heat, simultaneously with the compression ofcompression belt 57, to multi-overlapped nonwoven fabric strip 15. Athird heater array of infrared heaters 67 is shown in a position toapply heat, simultaneously with the compression of compression belt 59,to multi-overlapped nonwoven fabric strip 17.

Referring now to FIG. 4 of the drawings, numeral 71 designates amulti-stage winding machine for manufacturing multi-overlapped corelessfilter elements 11. A roll of nonwoven fabric strip 13 is shown mountedon a roll support 75 consisting of an upright member 77 onto which aremounted one or more cylindrical roll support shafts 79 extendingperpendicularly outward from the upright member 77 to receive thetubular core (not shown) of the roll of non-woven fabric strip 13. Eachroll support shaft 79 is connected to the upright member 77 at a pointalong the length of the upright member 77. The upright member 77 isconnected at its base to a plurality of horizontal legs (not shown)which extend perpendicularly outward to such length as to providesupport for the upright member 77, each roll support shaft 79, and eachroll non-woven the fabric strip 13 loaded onto each roll support shaft79.

A feed tray 81 consists of a rectangular plate with its two longestopposing edges 83 and 85 each turned up at a right angle so as to form achannel which supports and guides and is adjustable to the width of thenonwoven fabric strip 13. Each stage of the winding machine 71 has afeed tray 81 and a tensioner roller 147 connected to an air cylinder(not shown).

Heater array support 87, a mounting plate for the first heater array 63,stands vertically in a plane which is perpendicular to the axis 89 ofthe winding machine 71. The heater array support 87 is connected alongits base edge to a machine support structure 91 which extends parallelto the axis 89 of the winding machine 71 and supports each stagethereof. The heater array support 87 has an input surface (not shown)and an output surface 93. Connected to the output surface 93 andextending along the axis 89 and through each stage of the windingmachine 71 is a hollow mandrel 47. Attached to the input surface of theheater array support 87 is a conduit (not shown) for transporting theheat exchange medium from a pumping device (represented schematically inFIG. 7, numeral 324) to the heater array support 87, through an aperture(not shown) in the heater array support 87, and into the cylindricalchannel 53 (see FIG. 2) of the hollow mandrel 47. Connected to theoutput surface 93 of the heater array support 87 is a plurality ofheater actuators 97 each of which consists of a dial adjustmentmechanism 99 connected through a gear mechanism (not shown) to a heateractuator plate 101.

Attached to each heater actuator plate 101 and extending outward fromthe output surface 93 of the heater array support 87 and parallel to theaxis 89 of the winding machine 71 is an infrared heater 63. Eachinfrared heater 63 is attached to a corresponding heater actuator plate101 in such a fashion as to direct the heat perpendicular to and in thedirection of the hollow mandrel 47. Each infrared heater 63 extendsoutward from the output surface 93 of the heater array support 87 aselected distance.

A pair of capstans consisting of a driving capstan 105 and a drivencapstan 106 stand vertically with their axes (not shown) perpendicularto and on either side of the axis 89 of the winding machine 71. Thedriving capstan 105 is mounted onto a driving capstan gearbox 107 andthe driven capstan 106 is mounted onto a driven capstan gearbox 109. Thedriving capstan gearbox 107 is connected at its base to a gearboxplatform 113. The gearbox platform 113 is a rectangular plate that sitsatop the machine support structure 91 in a horizontal plane. A capstandriving motor (represented schematically in FIG. 7, numeral 314) ismounted underneath the gearbox platform 113 and has a shaft (not shown)which extends through an aperture (not shown) in the gearbox platform113 and connects to the gears of the driving capstan gearbox 107. Thedriving capstan gearbox 107 is connected to the driven capstan gearbox109 by a splined shaft (not shown in the first-stage, but identical tothe splined shaft 111 of the fourth stage) thereby providing a means fordriving the capstans 105 and 106 at the same angular speed but inopposing directions.

The driven capstan gearbox 109 is connected at its base to a gearboxsliding plate 115. The underside of the gearbox sliding plate 115 has aplurality of grooves that extend along its length and parallel to thelength of the gearbox platform 113. The grooves of the gearbox slidingplate 115 receive the rails of a digital linear encoder 117 therebyallowing the digital linear encoders 117 to incrementally measure thelocation of the driven capstan 109 along the rails of the digital linearencoder 117 relative to a reference point on the digital linear encoder117. The digital linear encoder 117 can be of the type disclosed in U.S.Pat. No. 4,586,760 or any other incremental linear measuring deviceknown to persons skilled in the art. Near the center of the gearboxplatform 113 and cut through the thickness of the platform is anarc-shaped slot (not shown in the first-stage, but identical to thearc-shaped slot 119 of the fourth stage), the chord of which is parallelto the length of the gearbox platform 113. A gearbox platform adjustmentset screw (not shown in the first stage, but identical to the gearboxplatform adjustment set screw 121 of the fourth stage) passes throughthe arc-shaped slot identical to slot 119 and is received into athreaded aperture (not shown) in the machine support structure 91. Theangle of the belt 55 relative to the mandrel 47 may be adjusted withthis mechanism.

Capstan sleeves 123 and 125 are concentric about the axes of the drivingcapstan 105 and the driven capstan 106, respectively. The radiallyinterior surfaces of the capstan sleeves 123 and 125 are mated with theradially exterior surfaces of the driving capstan 105 and the drivencapstan 106, respectively, and are attached thereto by suitable means ata selected location on the driving capstan 105 and on the driven capstan106. Annular capstan sleeve flanges 127 and 129 extend radially outwardfrom the driving capstan 105 and the driven capstan 106, respectively.

Compression belt 55 forms a closed loop around one half of the peripheryof the driving capstan 105 and one half of the periphery of the drivencapstan 106 and is placed in tension by the distance between the axes ofthe driving capstan 105 and the driven capstan 106. The compression beltcrosses over itself a single time between the driving capstan 105 andthe driven capstan 106. In addition, the compression belt 55 forms asingle spiral around the hollow mandrel 47.

A tensioner air cylinder 133 is mounted onto the gearbox platform 113 atthe same end as the driven capstan gearbox 109. The tensioner aircylinder 133 is a commonly used pneumatic cylinder with a shaft 135 thatextends from one end of the tensioner air cylinder 133 in parallel withthe length of the gearbox platform 113 and is connected at the opposingend to the driven capstan gearbox 109.

Three additional stages of the multi-stage winding machine 71 are shownin FIG. 4. Each such additional stage consists of identical componentsas the first stage with the exception that the heater array support 137of each additional stage includes an aperture 139 concentric about theaxis 89 of the winding machine 71 through which the hollow mandrel 47passes with sufficient clearance for bands 14, 16, 18, 20 of the filterelement 11; and with the exception that the feed tray 81 is replaced bya feed tensioner 141 consisting of a vertically upright member 143connected at its base to a plurality of horizontal legs 145 andconnected at the opposite end to feed tensioner rollers 147.

Referring now to FIG. 5 of the drawings, a block diagram of each step ofthe manufacturing process of the nonwoven fabric is illustrated. Eachsignificant step of the manufacturing process is depicted in a separateblock. In block 151, step 1 is the acquisition of fiber, usually in theform of a bale purchased from a textile fiber producer. Each strip 13,15, 17, 19 is composed of one or more fibers. If a strip 13, 15, 17, 19is composed of only one fiber, it should be of the type which consistsof a lower melting point outer shell and a higher melting point innercore. If a strip 13, 15, 17 19 is composed of two or more fibers, atleast one of the fibers must have a lower melting point than the othersor be of the shell and core type mentioned above.

In block 153, step 2 is opening and weighing of the fiber materials. Thefibers are transported to a synchro-blender where they are furtheropened in preparation for final blending in block 155.

In block 155, step 3 is the final blending of the fibers whereby theindividual fibers are thoroughly intermixed by a series of cylindricalrollers and lickerins to provide a homogeneous dispersion of fibers.This step is performed in a blender similar to the blender disclosed inU.S. Pat. No. 3,744,092.

In block 157, step 4 is the transportation of the thoroughly mixedfibers via an air duct system consisting of a duct approximately 12inches in diameter through which air is circulated at a rate ofapproximately 1,500 feet per minute from the blender to the feeder.

In block 159, step 5 is the feeding of the intermixed fibers into afeeder similar to the feeder disclosed in U.S. Pat. Nos. 2,774,294 and2,890,497.

Block 161, step 6 is a web formation step in which the fibers areconveyed from the feeder to a webber similar to the webber disclosed inU.S. Pat. Nos. 2,890,497 and 2,703,441, consisting of a plurality ofcylindrical rollers and a lickerin such that a continuous web of thehomogeneously dispersed fibers is formed.

Block 163, step 7 is a liquefaction and compression step carried out ina series of air-draft ovens and/or alternative heat sources in which aflow of air heated to a selected temperature is blown down onto the webthereby causing liquefaction of all or part of particular types of thehomogeneously dispersed fibers as more fully explained hereinafter.Simultaneously with the liquefaction of all or part of particular typesof the homogeneously dispersed fibers, is compression of thecontinuously formed web into a thin sheet. The air in the air-draftovens is saturated to near 100% with low pressure steam. Liquid water ispumped through pipes into the air-draft ovens where it spilled ontoheated stainless steel plates thereby creating low pressure steam. Thesaturation level required is dependent upon the temperature inside theair-draft ovens which ranges from 200° to 550° Fahrenheit. The steamneutralizes the static electricity created by the air which isrecirculated at rates of up to 40,000 cubic feet per minute. There is apressure differential across the web in the air-draft oven of between 4and 8 inches of water column. Residence time for the web in theair-draft ovens is dependent upon and coordinated with the dischargerate of the web being produced at the webber.

In block 165, step 8 is the compression of the sheet of homogeneouslydispersed fibers into a nonwoven fabric with a thickness required forthe desired filtration efficiency by conveying the sheet between twocylindrical stainless steel rollers.

In block 166, step 8-A, is the formation of a roller of the nonwovenfabric on a winder.

In block 167, step 9 of the manufacturing process is the formation ofstrips from the sheet of nonwoven fabric. Cutting devices are positionedat selected spots across the width of the sheet of nonwoven fabric so asto cut the sheet into a plurality of strips of selected widths therebyforming strips of nonwoven fabric such as 13, 15, 17, 19.

In block 169, step 10 the nonwoven strips 13, 15, 17, 19 are wound ontocores which are in the form of cylindrical tubes on a commonly knownwinder consisting of a plurality of cylindrical rollers for aligning andwinding the strips of nonwoven fabric 13, 15, 17, 19 onto cores.

The entire nonwoven sheet manufacturing process takes place in ahumidity-controlled environment. The relative humidity of the air in theenvironment ranges from 60% to 80% as measured by wet bulb/dry bulbthermometer and an enthalpy chart.

Referring now to FIG. 6 of the drawings, a schematic diagram of thepreferred computer based data processing and control system of thewinding machine 71 is illustrated. It should be understood that thewinding machine 71 may be manually operated. Data processing system 200is controlled primarily by computer readable instructions in the form ofsoftware such as Intellution written by Intellution, Inc. of Norwood,Mass. Such software is executed within central processing unit (CPU) 250to cause data processing system 200 to control selected functions ofwinding machine 71.

CPU 250 retrieves, decodes, and executes instructions, and transfersinformation to and from other resources via the computer's maindata-transfer path, system bus 254. System bus 254 connects thecomponents in the data processing system 200 and defines the medium fordata exchange. System bus 254 typically includes data lines for sendingdata, address lines for sending addresses, and control lines for sendinginterrupts and for operating the system bus.

Memory devices coupled to system bus 254 include random access memory(RAM) 256, read only memory (ROM) 258, and nonvolatile memory 260. Suchmemories include circuitry that allows information to be stored andretrieved. Data stored in RAM 256 can be read or changed by CPU 250 orother hardware devices. ROM 258 contains stored data that cannot bemodified. Nonvolatile memory is memory that does not lose data whenpower is removed from it. Nonvolatile memories include ROM, EPROM, flashmemory, bubble memory, or battery-backed CMOS RAM 260. Battery-backedCMOS RAM 260 may be utilized to store system configuration information.

Access to RAM 256, ROM 258, and nonvolatile memory 260 may be controlledby memory controller 262 and bus controller 264. Memory controller 262may provide an address translation function that translates virtualaddresses into physical addresses as instructions are executed. Memorycontroller 262 may also provide a memory protection function thatisolates processes within the system and isolates system processes fromuser processes. Thus, a program running in user mode can access onlymemory mapped by its own process virtual address space; it cannot accessmemory within another process's virtual address space unless memorysharing between the processes has been set up.

An expansion card or expansion board is a circuit board that includeschips and other electronic components connected in a circuit that addsfunctions or resources to the computer. Typical expansion cards addmemory, disk-drive controllers 266, video support, parallel and serialports, and internal modems. Thus, empty slots 268 may be used to receivevarious types of expansion cards.

Disk controller 266 and diskette controller 270 both includespecial-purpose integrated circuits and associated circuitry that directand control reading from and writing to a hard disk drive 272 and afloppy disk or diskette 274, respectively. Such disk controllers handletasks such as positioning read/write head, mediating between the driveand the microprocessor, and controlling the transfer of information toand from memory. A single disk controller may be able to control morethat one disk drive.

A CD-ROM controller 276 may be included in the data processing system200 for reading data from (compact disk read-only memory) CD-ROM 278.Such CD-ROM disks 278 use laser optics rather than magnetic means forreading data. Keyboard mouse controller 280 is provided in the dataprocessing system 200 for interfacing with keyboard 282 and a pointingdevice, such as mouse 284. Such pointing devices are typically utilizedto control an on-screen element, such as a cursor, which may take theform of an arrow having a hot spot that specifies the location of thepointer when the user presses a mouse button.

Direct memory access (DMA) controller 286 may be used to provide amemory access that does not involve CPU 250. Such memory accesses aretypically employed for data transfer directly between memory and an"intelligent" peripheral device, such as between RAM 256 and diskcontroller 266.

Communication between data processing system 200 and other dataprocessing systems may be facilitated by serial controller 288 andnetwork adaptor 290, both of which are coupled to system bus 254. Serialcontroller 288 is utilized to transmit information between computers, orbetween a computer and peripheral devices, one bit at a time over asingle line. Serial communications can be synchronous (controlled bysome time standard such as a clock) or asynchronous (managed by theexchange of control signals that govern the flow of information).

Such a serial interface may be utilized to communicate with modem 292. Amodem is a communications device that enables a computer to transmitinformation over a standard telephone line. Modems convert digitalcomputer signals to analog signals suitable for communication overtelephone lines. Modem 292 may provide a connection to other sources ofsoftware, such as a file server, an electronic bulletin board, and theInternet or World Wide Web.

Network adaptor 290 may be used to connect the data processing system200 to a local area network (LAN) 294. LAN 294 may provide computerusers with means of communicating and transferring software andinformation electronically. Additionally, LAN 294 may providedistributed processing, which involves several computers and the sharingof workloads or cooperative efforts in performing a task.

Display 296, which is controlled by display controller 298, is used todisplay visual output generated by the data processing system 200. Suchvisual output may include text, graphics, animated graphics, and video.Display 296 may be implemented with a CRT-based video display, anLCD-based flat-panel display, or a gas plasma-based flat-panel display.Display controller 298 includes electronic components required togenerate a video signal that is sent to display 296.

Printer 300 may be coupled to the data processing system 200 viaparallel controller 302. Printer 300 is used to put text or acomputer-generated image onto paper or on another medium, such as atransparency. Other types of printers may include an image setter, aplotter, or a film recorder.

Parallel controller 302 is used to send multiple data and control bitssimultaneously over wires connected between system bus 254 and anotherparallel communication device, such as printer 300. The most commonparallel interface is the Centronics interface.

During data processing operations, the various devices connected tosystem bus 254 may generate interrupts which are processed by interruptcontroller 304. An interrupt is a request for attention from CPU 250that can be passed to CPU 250 by either hardware or software. Aninterrupt causes the microprocessor to suspend currently executinginstructions, save the status of the work in progress, and transfercontrol to a special routine, known as an interrupt handler, that causesa particular set of instructions to be carried out. Interrupt controller304 may be required to handle a hierarchy of interrupt priorities andarbitrate simultaneous interrupt requests. Interrupt controller 304 mayalso be used to temporally disable interrupts.

Referring now to FIG. 7 of the drawings, a schematic diagram of thecomponent control system of the winding machine 71 is illustrated.Component control system 305 is controlled primarily by computerreadable instructions in the form of software. Such software is executedwithin control Programmable Logic Controller (PLC) 306 to activatecomponent control system 305.

The control PLC 306 retrieves, decodes, executes instructions, andtransfers information to and from other resources via the componentcontrol system's main data-transfer path, logic control bus 308. Thelogic control bus 308 connects the components in the component controlsystem 305 and defines the medium for data exchange. The logic controlbus 308 typically includes data lines for sending data, address linesfor sending addresses, and control lines for sending interrupts and foroperating the logic control bus 308.

Communication between component control system 305 and data processingsystem 200 is facilitated by serial controller 288 which is coupled toserial controller 307. Serial controller 288 is utilized to transmitinformation between the data processing system 200 and the componentcontrol system 305, through serial controller 307, one bit at a timeover a single line. A plurality of digital logic controllers 310, 311,313, 315, 317, 319 are in communication with the control PLC 306 via thelogic control bus 308.

Digital logic controller 310 is in communication with motor control box312 which is coupled to and receives data from and transmits operationalinputs to one or more capstan driving motors 314 of the winding machine71. Digital logic controller 311 is in communication with digital linearencoder control box 316 which is coupled to and receives data from oneor more digital linear encoders 117 of the winding machine 71. Digitallogic controller 313 is in communication with tensioner air cylindercontrol box 318 which is coupled to and receives data from and transmitsoperational inputs to one or more tensioner air cylinders 133 of thewinding machine 71. Digital logic controller 315 is in communicationwith heater array control box 320 which is coupled to and transmitsoperational inputs to heater arrays 63, 65, 67, 68 of the windingmachine 71. Digital logic controller 317 is in communication with heattransfer medium pump control box 322 which is coupled to and receivesdata from and transmits operational inputs to the heat transfer mediumpump 324 of the winding machine 71. Digital logic controller 319 is incommunication with temperature detecting device control box 323 which iscoupled to and receives data from temperature detecting device 326 ofthe winding machine 71.

Each non-woven fabric strip 13, 15, 17, 19, is composed of selectedpolymeric fibers such as polyester and polypropylene which serve as bothbase fibers and binder fibers. Base fibers have higher melting pointsthan binder fibers. The role of base fibers is to produce small porestructures in the coreless filter element 11. The role of the binderfiber or binder material is to bond the base fibers into a rigid filterelement that does not require a separate core. The binder fibers mayconsist of a pure fiber or of one having a lower melting point outershell and a higher melting point inner core. If the binder fiber is ofthe pure type, then it will liquify throughout in the presence ofsufficient heat. If the binder fiber has an outer shell and an innercore, then it is subjected to temperatures that liquify only the outershell in the presence of heat, leaving the inner core to assist the basefiber in producing small pore structures. The role therefor of thebinder fiber is to liquefy either in whole or in part in the presence ofheat, the liquid fraction thereof to wick onto the base fibers to form abond point between the base fibers, thereby bonding the base fiberstogether upon cooling. The binder material may be in a form other thanfibrous.

Referring now to the preferred embodiment of the invention, the basefibers and binder fibers are blended according to the manufacturingprocess set forth in FIG. 5 to form rolls of non-woven fabric strips 13,15, 17, 19, each of a selected composition. Upon completion of themanufacture of rolls of nonwoven fabric strips 13, 15, 17, 19, the rollsthereof are loaded onto the roll support shafts 79 of the roll support75 at each stage of the winding machine 71. Each roll support 75 ispositioned to introduce the non-woven fabric strips 13, 15, 17, 19, at aselected angle to the hollow mandrel 47. The desired specifications fora multi-overlapped coreless filter element 11 are selected via thekeyboard 282 or mouse 284 of the data processing system 200. Accordingto the software, the CPU 250 retrieves, decodes, executes instructions,and transmits the appropriate information to the control PLC 306 of thecomponent control system 305. The control PLC 306 retrieves, decodes,executes instructions, and transmits control information to the digitallogic controllers 310, 311, 313, 315, 317, 319, which in turn analyzeand format the control information. The control information iscommunicated to the appropriate motor control box 312, tensioner aircylinder control box 318, heater array control box 320, or heat transfermedium pump control box 322, which converts the control information intooperational inputs and sends the operational inputs to the appropriatecapstan driving motor 314, tensioner air cylinder 133, heater arrays 63,65, 67, 68, or heat transfer medium pump 324, each of which operates andperforms work according to the operational inputs.

A length of the non-woven fabric strip 13 is unrolled and fed over thefeed tray 81 such that it lies between the upturned edges 83 and 85 ofthe feed tray 81. The feed tray 81 is positioned such that the non-wovenfabric strip 13 is introduced to the hollow mandrel 47 at a selectedangle. According to the operational inputs from the motor control box312, the capstan driving motor (represented schematically in FIG. 7,numeral 314) turns the gears of the driving capstan gearbox 107 whichturns the driving capstan 105. The splined shaft of the first stage ofthe winding machine 71 transmits power to the driven capstan gearbox109, the gears of which turn the driven capstan 106 at the same angularspeed but in the opposite direction as the driving capstan 105. Frictionbetween the interior surface of the compression belt 55 and the radiallyexterior surfaces of the driving capstan 105 and the driven capstan 106allows the belt to turn with the capstans 105 and 106 without tangentialslippage. The capstan sleeve flanges 127 and 129 of the capstan sleeves123 and 125, respectively, prohibit the compression belt 55 fromdownward slippage on the driving and driven capstans 105 and 106,respectively.

The leading edge 31 of the non-woven fabric strip 13 is then fed betweenthe annular exterior surface 49 of the hollow mandrel 47 and thecompression belt 55 at the point where the compression belt 55 makes itssingle spiral loop around the hollow mandrel 47. Because the frictiondrag generated between the compression belt 55 and the non-woven fabricstrip 13 is greater than the friction drag generated between thenon-woven fabric strip 13 and the hollow mandrel 47, the coreless filterelement 11 is formed in a conical helix shape and is driven along thehollow mandrel 47 toward the free end thereof. The feed angle betweenthe non-woven fabric strip 13 and the hollow mandrel 47 is such that thenon-woven fabric strip 13 overlaps itself a plurality of times as it iscompressed between the compression belt 55 and the hollow mandrel 47producing the multi-overlapped conical helix feature of the presentinvention. The source of the selected compressive force of thecompression belt 55 is the tension in the compression belt 55 which isdetermined by the selected distance between the axes of the drivingcapstan 105 and the driven capstan 106. Since the driven capstan 106 isconnected to the driven capstan gearbox 109 which is connected at itsbase to the gearbox sliding plate 115, the driven capstan 106 is free totranslate along the rails of the digital linear encoder 117. The digitallinear encoder 117 is coupled to a digital linear encoder control box316 whereby it transmits data to a digital logic controller 311 and acontrol PLC 306. The digital linear encoder 117 incrementally measuresthe location of the driven capstan gearbox 109 along the rails of thedigital linear encoder 117 relative to a reference point on the digitallinear encoder 117 and transmits that information to the componentcontrol system 305. The location of the driven capstan gearbox 109 istransmitted to the component control system 305 whereby the speed of thecapstan driving motor 314 is calculated and transmitted through themotor control box 312 to the capstan driving motor 314. The compressiveforce delivered by compression belt 55 to the nonwoven fabric strip 13is controlled and maintained by a selected pressure in the pneumatictensioner air cylinder 133, the shaft 135 of which is connected to thebase of the driven capstan gearbox 109. The pneumatic tensioner cylinder133 is coupled to a tensioner air cylinder control box 318 whereby itreceives operational inputs from a digital logic controller 313 and acontrol PLC 306. The pressure in the pneumatic tensioner air cylinder133 is adjusted according to the operational inputs such that its shaft135 is either extended or retracted thereby controlling and maintainingthe compressive force delivered by compression belt 55 to the nonwovenfabric strip 13.

Applied simultaneously with the aforementioned compression to themulti-overlapped non-woven fabric strip 13 is a selected amount of heatgenerated by an array infrared heaters 63 located a selected distancefrom the non-woven fabric strip 13. Each infrared heater 63 is connectedto a heater actuator plate 101 which provides for movement of eachinfrared heater 63 toward or away from the hollow mandrel 47. The dialadjustment mechanism 99 of the heater actuator plate 101 allows forincremental adjustment of the distance between each infrared heater 63and the hollow mandrel 47. Each infrared heater 63 is coupled to aheater array control box 320 whereby it receives operational inputs froma digital logic controller 315 and a control PLC 306, as to a selectedvoltage of electricity to be supplied to and maintained at each infraredheater 63 for the purpose of heating the multi-overlapped non-wovenfabric strip 13 to a selected temperature such that the base fibers ofthe multi-overlapped non-woven fabric strip 13 are bonded together bothwithin the strip and between the multi-overlapped layers of band 14 bythe wicking process of the liquified binder fibers.

As the non-woven fabric strip 13 is simultaneously heated and compressedto produce the desired porosity, a heat exchange medium is pumpedthrough the cylindrical channel 53 of the hollow mandrel 47 by a pumpingdevice (represented schematically in FIG. 7, numeral 324) at a selectedflow rate for the purpose of maintaining a selected temperature on theexterior surface 49 of the hollow mandrel 47. The pumping device iscoupled to a heat transfer medium pump control box 322 whereby itreceives operational inputs from a digital logic controller 317 and acontrol PLC 306, as to the selected flow rate to be imparted to the heatexchange medium so as to maintain a selected temperature at the exteriorsurface 49 of the hollow mandrel 47. One or more temperature detectingdevices such as thermocouples (not shown but represented schematicallyin FIG. 7, numeral 326) are in communication with the heat exchangemedium for the purpose of detecting the temperature of the heat exchangemedium. Each temperature detecting device is coupled to a temperaturedetecting device control box 323 whereby it transmits data relating tothe temperature of the heat transfer medium to a digital logiccontroller 319 and a control PLC 306.

The component control system 305 continuously receives and analyzessignals from the capstan driving motor 314, digital linear encoder 117,tensioner air cylinder 133, heat transfer medium pump 324, and thetemperature detecting device 326 enabling the component control system305 to continuously transmit updated operational inputs to the capstandriving motor 314, tensioner air cylinder 133, heater arrays 63, 65, 67,68, and heat transfer medium pump 324. The data transmitted from thedigital linear encoder 117 of each stage of the winding machine 71 isused to calculate and determine the speed of the capstan driving motor314 of each stage, thereby synchronizing the speed of each capstandriving motor with the first-stage capstan driving motor 314.

The non-woven fabric strip 13 continues to be overlapped upon itselfthereby forming band 14 which is driven along the hollow mandrel 47through the apertures 139 of the heater array supports 137 of eachremaining stage of the winding machine 71 in a continuous unendingfashion. Once band 14 has passed through all stages of the windingmachine 71 a length of the second-stage non-woven fabric strip 15 isunrolled and fed between the feed tensioner rollers 147 of a feedtensioner 141. The leading edge 35 of the non-woven fabric strip 15 isthen fed between the compression belt 57 and the annular exteriorsurface of band 14 at the point where the compression belt 57 makes itssingle spiral around the hollow mandrel 47.

The nonwoven fabric strip 15 is simultaneously compressed and heated byidentical means as the first-stage nonwoven fabric strip 13. Thenon-woven fabric strip 15 continues to be overlapped upon itself,thereby forming band 16, the annular interior surface of which is bondedto the annular exterior surface of band 14. The combined bands 14 and 16are driven along the hollow mandrel 47 through the apertures 139 of theheater array supports 137 of each remaining stage of the winding machine71 in a continuously unending fashion. Once the combined bands 14 and 16have passed through all remaining stages of the winding machine 71 alength of the third-stage non-woven fabric strip 17 is unrolled and fedbetween the feed tensioner rollers 147 of a feed tensioner 141. Theleading edge 39 of the non-woven fabric strip 17 is then fed between thecompression belt 59 and the annular exterior surface of band 16 at thepoint where the compression belt 59 makes its single spiral around thehollow mandrel 47.

The nonwoven fabric strip 17 is simultaneously compressed and heated byidentical means as the first-stage nonwoven fabric strip 13. Thenon-woven fabric strip 17 continues to be overlapped upon itself,thereby forming band 18, the annular interior surface of which is bondedto the annular exterior surface of band 16. The combined bands 14, 16,18 are driven along the hollow mandrel 47 through the apertures 139 ofthe heater array supports 137 of each remaining stage of the windingmachine 71 in a continuously unending fashion. Once the combined bands14, 16, 18 have passed through all remaining stages of the windingmachine 71 a length of the fourth-stage non-woven fabric strip 19 isunrolled and fed between the feed tensioner rollers 147 of a feedtensioner 141. The leading edge 43 of the non-woven fabric strip 19 isthen fed between the compression belt 61 and the annular exteriorsurface of band 18 at the point where the compression belt 61 makes itssingle spiral around the hollow mandrel 47.

The non-woven fabric strip 19 continues to be overlapped upon itself,thereby forming band 20, the annular interior surface of which is bondedto the annular exterior surface of band 18. The combined bands 14, 16,18, 20 are driven along the hollow mandrel 47 in a continuously unendingfashion toward a measuring device (not shown) and a cutting device (notshown). Once the combined bands 14, 16, 18, and 20 have passed throughthe final stage of the winding machine 71, the filter element 11 ismeasured by the measuring device and cut to length by the cuttingdevice.

The angular speed of the capstan driving motor is such that thenon-woven fabric strips 13, 15, 17, 19 remain in close enough proximityto the infrared heaters 63, 65, 67, 68 for a selected duration of timeso as to allow proper liquefaction of the binder fibers. Also,sufficient distance between stages is provided so that the binder fibersare allowed to partially cool thereby bonding the base fibers withineach nonwoven strip 13, 15, 17, 19, between each layer thereof, andbetween each band 14, 16, 18, 20, providing the desired porosity betweeneach layer and between each band 14, 16, 18, 20.

The simultaneous application of selected amounts of heat and compressionto the layers of non-woven fabric strips 13, 15, 17, 19, is such thatonly selected properties are altered resulting in a coreless filterelement 11 with sufficient structural strength to be self-supporting,i.e., requiring no structural core, while maintaining the desiredporosity.

The simultaneous application of selected amounts of heat and compressionto the non-woven fabric strips 13, 15, 17, 19, as described above, allowfor systematic variation of the density of the layers of non-wovenfabric strips 13, 15, 17, 19, across the wall of the filter element andthe systematic variation of the porosity of the base fibers, of theelement 11.

The direction of flow of filtrate through the filter element 11 can beeither from the core toward the annular outside wall or from the annularoutside wall toward the core, but in either case the filtrate flow isgenerally perpendicular to the axis of the filter element 11. However,due to the conical helix nature of the layers of non-woven fabric strips13, 15, 17, 19, the pores formed by the bonded base fibers lie at anangle to the axis of the filter element 11 making it more difficult forlarge particles of filtrate to pass through the filter element 11.

The filter element 11 may be finished by capping the ends 25 and 27 byany suitable means known to persons skilled in the art, such as pottingin a polymeric resin.

A cable-activated kill switch (not shown) extends over the length of thewinding machine 71 for the purpose of halting the winding machine 71.

An example of the method and means of manufacturing a filter element ofthe type shown in FIG. 1 is as follows: Four different types of fiberswere purchased from Hoechst Celanese of Charlotte, N.C., sold under thefiber designation "252," "121," "224," and "271". Fiber "252" was of thecore and shell type, whereas fibers "121," "224," and "271" were of thesingle component pure type. The denier of fiber "252" was 3 and itslength was 1.500 inches. The denier of fiber "121" was 1 and its lengthwas 1.500 inches. The denier of fiber "224" was 6 and its length was2.000 inches. The denier of fiber "271" was 15 and its length was 3.000inches. A first blend of fibers was manufactured from fiber "121" andfiber "252" composed of 50% by weight of each fiber type. A second blendof fibers was manufactured from fiber "224" and fiber "252" composed of50% by weight of each fiber type. A third blend of fibers wasmanufactured with a composition of 25% by weight of fiber "121" and 25%by weight of fiber "224" and 50% by weight of fiber "252". A fourthblend of fibers was manufactured from fiber "271" and fiber "252"composed of 50% by weight of each fiber type. Fiber "252" being of thecore and shell type served as the binder fiber in each of theaforementioned blends. Each blend of fibers was manufactured accordingto the process set forth in FIG. 5. Each blend of fibers was formed intoa web which was approximately 1/2 inch in thickness. The thickness ofeach web was reduced by approximately 50% forming a mat during itsresidence time of ninety seconds in the air draft ovens due to therecirculation of steam-saturated air at approximately 40,000 cubic feetper minute at a temperature of 400 degrees Fahrenheit. There was adifferential pressure across the mat in the air draft ovens of 6 inchesof water. Upon exiting the air draft ovens, each mat was fed between twostainless steel cylindrical rollers which compressed the thickness ofeach mat by approximately 50% into a sheet of nonwoven fabric with awidth of about 37 inches. Each 37-inch wide sheet of nonwoven fabric wascut into 6-inch wide strips 13, 15, 17, 19. The basis weight of eachsheet of nonwoven fabric was determined and to be in the range of 0.5 to1.2 ounces per square foot. As a quality assurance step, once the stripsof nonwoven fabric were cut, they were tested on a Frasier air flowtester to determine air permeability in cubic feet per minute per squarefoot. The strips of nonwoven fabric 13, 15, 17, 19 were then loaded ontothe roll support shafts 79 of the roll support 75, one roll at eachstage of the winding machine 71.

The specifications of the strips of nonwoven fabric 13, 15, 17, 19 wereinput into the data processing system 200 with the keyboard 282 and themouse 284. The hollow mandrel 47 was made of stainless steel and had anominal outside diameter of 1 inch. The heat transfer medium pumpingdevice 324 was started and began pumping the heat transfer mediumthrough the hollow mandrel 47 at varying flow rates such that thetemperature of the annular exterior surface 49 of the hollow mandrel 47was maintained at 200 degrees Fahrenheit, according to data transmittedfrom the temperature detecting device 326 to the component controlsystem 305 and operational inputs from the component control system 305.The first-stage capstan driving motor 314 was started at a control speedof approximately 50 hertz, as instructed by the component control system305. The first-stage heater array 63 was turned on and supplied with avoltage of electricity sufficient to create a temperature at the hollowmandrel 47 of 300 degrees Fahrenheit.

The first band 14 of nonwoven fabric strip 13 was initiated by feedingthe nonwoven fabric strip 13 between the hollow mandrel 47 and thefirst-stage compression belt 55. The nonwoven fabric strip 13 washelically wound in an overlapping fashion upon itself forming band 14 asit was driven under the compression belt 55 and along the hollow mandrel47. As the outside diameter of band 14 increased, the driven capstan 106moved toward the driving capstan 105 so as to shorten the distancetherebetween and maintain a pressure of 10 pounds per square inchexerted on band 14 from compressed belt 55. This compression pressurewas a result of the tension in the compression belt 55 which wasdeveloped by the pressure in the tensioner air cylinder 133 of 50 poundsper square inch gage. The movement of the driven capstan 106 wasaccomplished by altering the pressure in the tensioner air cylinder 133.The digital linear encoder 117 detected the movement of the drivencapstan 106 thereby transmitting the outside diameter of band 14 to thecomponent control system 305 so that appropriate modifications to thespeed of the capstan driving motor 314 could be made by the componentcontrol system 305. The temperature created by the infrared heater 63was the "ironing point" temperature. This ironing point temperature of300 degrees Fahrenheit assisted compression and bonding of the basefibers between the layers of band 14. Under this simultaneousapplication of heat and compression, the thickness of the strips ofnonwoven fabric 13 was compressed by approximately 50% and there existedinterlayer bonding.

The band 14 was allowed to travel through each stage of the windingmachine 71 and prior to encountering the compression belt at each stage,the capstan driving motor at that stage was turned on and set to thespeed of the first-stage capstan driving motor 314 via operationalinputs from the component control system 305.

Once the band 14 progressed through all stages of the winding machine71, the second band 16 of nonwoven fabric strip 15 was initiated byfeeding the nonwoven fabric 15 between the second-stage compression belt57 and the annular exterior surface of band 14. The nonwoven fabric 15was helically wound in an overlapping fashion upon itself forming band16 as it was driven under compression belt 57 and along the hollowmandrel 47. The second-stage heater array 65 was turned on and suppliedwith a voltage of electricity sufficient to maintain an ironing pointtemperature of 300 degrees Fahrenheit at the annular exterior surface ofband 16. As the outside diameter of band 16 increased, the second-stagedriven capstan moved toward the second-stage driving capstan so as toshorten the distance therebetween and maintain a pressure of 10 poundsper square inch exerted on band 16 from compression belt 57. Thiscompression pressure was a result of the tension in the compression belt57 which was developed by the pressure in the second-stage tensioner aircylinder of 50 pounds per square inch gage. The movement of thesecond-stage driven capstan was accomplished by altering the pressure inthe second-stage tensioner air cylinder. The second-stage digital linearencoder detected the movement of the second-stage driven capstan therebytransmitting the outside diameter of band 16 to the component controlsystem 305 so that appropriate modifications to the speed of thesecond-stage capstan driving motor could be made by the componentcontrol system 305 to synchronize the speed of the second-stage capstandriving motor with the first-stage capstan driving motor 314. Theironing point temperature of 300 degrees Fahrenheit assisted compressionand bonding of the base fibers between the layers of band 16. Under thissimultaneous application of heat and compression, the thickness of thenonwoven fabric strip 15 was compressed by approximately 50% and thereexisted interlayer bonding. The annular interior surface of band 16 wasbonded to the annular exterior surface of band 14 and band 16 progressedalong the hollow mandrel 47 toward the third-stage compression belt 59.The band 16 was allowed to travel through the remaining stages of thewinding machine 71 and prior to encountering the compression belt ateach stage, the capstan driving motor at that stage was turned on andset to the speed of the second-stage capstan driving motor 314 viaoperational inputs from the component control system 305.

Once the band 16 progressed through all the stages of the windingmachine 71, the third band 18 of nonwoven fabric 17 was initiated byfeeding the nonwoven fabric strip 17 between the third-stage compressionbelt 59 and the annular exterior surface of band 16. The nonwoven fabric17 was helically wound in an overlapping fashion upon itself formingband 18 as it was driven under compression belt 59 and along the hollowmandrel 47. The third-stage heater array 67 was turned on and suppliedwith a voltage of electricity sufficient to maintain an ironing pointtemperature of 300 degrees at the annular exterior surface of band 18.As the outside diameter of band 18 increased, the third-stage drivencapstan moved toward the third-stage driving capstan so as to shortenthe distance therebetween and maintain a pressure of 10 pounds persquare inch exerted on the band 18 from compression belt 59. Thiscompression pressure was a result of the tension in the compression belt59 which was developed by the pressure in the third-stage tensioner aircylinder of 50 pounds per square inch gage. The movement of thethird-stage driven capstan was accomplished by altering the pressure ofthe third-stage tensioner air cylinder. The third-stage digital linearencoder detected the movement of the third-stage driven capstan therebytransmitting the outside diameter of band 18 to the component controlsystem 305 so that appropriate modifications to the speed of thethird-stage capstan driving motor could be made by the component controlsystem 305 to synchronize the speed of the third-stage capstan drivingmotor with the first-stage capstan driving motor 314. The ironing pointtemperature of 300 degrees Fahrenheit assisted compression and bondingof the base fibers between the layers of band 18. Under thissimultaneous application of heat and compression, the thickness ofnonwoven fabric strip 17 was compressed by approximately 50% and thereexisted interlayer bonding. The annular interior surface of band 18 wasbonded to the annular exterior surface of band 16 and band 18 progressedalong the hollow mandrel 47 toward the fourth stage compression belt 61.The band 18 was allowed to travel through the remaining stage of thewinding machine 71 and prior to encountering the fourth-stagecompression belt, the fourth-stage capstan driving motor was set to thespeed of the third-stage capstan driving motor via operational inputsfrom the component control system 305.

Once the band 18 progressed through all the remaining stage of thewinding machine 71, the fourth band 20 of nonwoven fabric strip 19 wasinitiated by feeding the nonwoven fabric strip 19 between thefourth-stage compression belt 61 and the annular exterior surface ofband 18. The nonwoven fabric strip 19 was helically wound in anoverlapping fashion upon itself forming band 20 as it was driven undercompression belt 61 and along the hollow mandrel 47. The fourth-stageheater array 68 was turned on and supplied with a voltage of electricitysufficient to maintain an ironing point temperature of 300 degrees atthe annular exterior surface of band 20. As the outside diameter of band20 increased, the fourth-stage driven capstan moved toward thefourth-stage driving capstan so as to shorten the distance therebetweenand maintain a pressure of 10 pounds per square inch exerted on the band20 from compression belt 61. This compression pressure was a result ofthe tension in the compression belt 61 which was developed by thepressure in the fourth-stage tensioner air cylinder of 50 pounds persquare inch gage. The movement of the fourth-stage driven capstan wasaccomplished by altering the pressure of the fourth-stage tensioner aircylinder. The fourth-stage digital linear encoder detected the movementof the fourth-stage driven capstan thereby transmitting the outsidediameter of band 20 to the component control system 305 so thatappropriate modifications to the speed of the fourth-stage capstandriving motor could be made by the component control system 305 tosynchronize the speed of the fourth-stage capstan driving motor with thefirst-stage capstan driving motor 314. The ironing point temperature of300 degrees Fahrenheit assisted compression and bonding of the basefibers between the layers of band 20. Under this simultaneousapplication of heat and compression, the thickness of nonwoven fabricstrip 19 was compressed by approximately 50% and there existedinterlayer bonding. The annular interior surface of band 20 was bondedto the annular exterior surface of band 18 and band 20 progressed alongthe hollow mandrel 47 toward the measuring and cutting devices wherebyit was measured and cut to a length of 30 inches.

The resulting filter element 11 had a 1-inch nominal inside diameter, a2.5-inch nominal outside diameter and was cut to 30 inches long. Itweighed one pound and had an airflow capacity of 20 cubic feet perminute, producing a 4.9 inches of water column differential pressure.

In an alternate embodiment of the invention, an idler belt may beincluded at one or more stages of the multi-stage winding machine 71 soas to maintain the hollow mandrel 47 in a properly fixed position.

In an alternate embodiment of the invention, a plurality of non-wovenfabric strips are added in a single stage of the multi-stage windingmachine 71.

While the invention is shown in only one of its forms, it is not justlimited but is susceptible to various changes and modifications withoutdeparting from the spirit thereof.

We claim:
 1. A coreless filter element comprising:a nonwoven fabriccomprising a substantially homogeneous mixture of a base fiber and abinder material compressed to form a first nonwoven fabric strip ofselected porosity; the first nonwoven fabric strip being spirally woundupon itself in multiple overlapping layers to form a first band having aselected radial thickness; a second nonwoven fabric comprising asubstantially homogeneous mixture of a base fiber and a binder fibercompressed to form a second nonwoven fabric strip of selected porositywhich differs from the porosity of the first fabric strip; the secondfabric strip being spirally wound upon itself in multiple overlappinglayers to form a second band having a selected radial thickness; thefirst and second bands being overlapped and bonded to form a porous,self-supporting filter element.
 2. A coreless filter elementcomprising:a nonwoven fabric comprising a substantially homogeneousmixture of a base fiber and a binder material compressed to form a firstnonwoven fabric strip of selected porosity; the binder material havingat least a surface with a melting temperature lower than that of thebase fiber, the base fiber and the binder material being thermally fusedat a temperature to melt at least the surface of the binder material tobind the base fibers, when the fabric is cooled, into the first nonwovenfabric strip; the first nonwoven fabric strip being spirally wound uponitself in multiple overlapping layers to form a first band having aselected radial thickness; a second nonwoven fabric comprising asubstantially homogeneous mixture of a base fiber and a binder fibercompressed to form a second nonwoven fabric strip of selected porosity;the binder material of the second nonwoven fabric having at least asurface with a melting temperature lower than that of the base fiber,the base fiber and the binder material being thermally fused at atemperature to melt at least the surface of the binder material to bindthe base fibers, when the sheet is cooled, into the second nonwovenfabric strip; the second fabric strip being spirally wound upon itselfin multiple overlapping layers to form a second band having a selectedradial thickness; the first and second bands being overlapped and bondedto form a porous, self-supporting filter element.
 3. The coreless filterelement of claim 2, wherein the first and second nonwoven fabric stripsare helically wound and thermally fused and compressed to form a tubularfilter element.
 4. The coreless filter element of claim 3, wherein thefirst and second nonwoven fabric strips have differing porosities. 5.The coreless filter element of claim 4, wherein the filter element iscomprised of three or more overlapped bands of multi-overlapped nonwovenfabric strips.
 6. A coreless filter element comprising:a nonwoven fabriccomprising a substantially homogeneous mixture of a base fiber and abinder material thermally fused and compressed to form a first nonwovenfabric strip of selected porosity; the binder material having at least asurface with a melting temperature lower than that of the base fiber,the base fiber and the binder material being thermally fused at atemperature to melt at least the surface of the binder material to bindthe base fibers, when the fabric is cooled, into the first nonwovenfabric strip; the first nonwoven fabric strip being spirally wound uponitself in multiple overlapping layers to form a first band having aselected radial thickness and an axial length; at least a secondnonwoven fabric comprising a substantially homogeneous mixture of a basefiber and a binder fiber thermally fused and compressed to form a secondnonwoven fabric strip of selected porosity; the binder material of thesecond nonwoven fabric having at least a surface with a meltingtemperature lower than that of the base fiber, the base fiber and thebinder material being thermally fused at a temperature to melt at leastthe surface of the binder material to bind the base fibers, when thefabric is cooled, into the second nonwoven fabric strip; the secondfabric strip being spirally wound upon itself in multiple overlappinglayers to form a second band having a selected radial thickness; thesecond fabric strip being overlapped along at least a portion of theaxial length of the first fabric strip and again fused at a temperatureto melt at least a surface of the binder material in the nonwoven fabricstrips to bind the base fibers of the first and second bands into aporous, self-supporting filter element.
 7. The coreless filter elementof claim 6, wherein the first and second nonwoven fabric strips arehelically wound and thermally fused and compressed to form a tubularfilter element.
 8. The coreless filter element of claim 7, wherein thefirst and second nonwoven fabric strips have differing porosities. 9.The coreless filter element of claim 8, wherein the filter element iscomprised of three or more overlapped bands of multi-overlapped nonwovenfabric strips.
 10. The coreless filter element of claim 9, wherein eachband includes at least three overlapped layers which give the band theselected radial thickness.
 11. The coreless filter element of claim 10,wherein each band includes five overlapped layers which give the